In recent years, in association with the rapid progress of an aging society or a rise in chronic diseases such as lifestyle-related diseases, the risk of contracting deep mycosis and superficial mycosis caused by pathogenic fungi has also increased. Serious deep mycosis, such as invasive candidiasis, often threatens human life. The principal defensive mechanism of a host organism against fungi such as candida is originally considered to be brought about by nonspecific immunity mediated by neutrophils. When this defensive mechanism functions normally, there is a low risk of being infected by fungi. In recent years, however, the risk of contracting deep mycosis has been increased due to the increased number of patients having underlying diseases, such as malignant tumor and AIDS, which reduce the immune functions of organisms, frequent use of anticancer agents, immunosuppressants or the like, heavy use of antibacterial antibiotic substances or steroid hormones, long-term use of parenteral nutrition and intravenous catheters, etc. (Non Patent Document 1).
Only 9 types of drugs are available for such deep mycosis: amphotericin B, flucytosine, miconazole, fluconazole, itraconazole, voriconazole, posaconazole, caspofungin and micafungin. Amphotericin B has very strong antiseptic effects, but disadvantageously has adverse reactions such as renal toxicity resulting in limited clinical use. Flucytosine presents problems such as resistance and is therefore rarely used alone in current practice. Caspofungin and micafungin are weakly active against the genus Cryptococcus. All of the other drugs are collectively referred to as azole antifungal agents. These agents generally tend to be inferior in antiseptic effects on fungi to amphotericin B and however, are currently used most frequently in light of efficacy-safety tradeoffs (Non Patent Document 2).
Recently, fluconazole-resistant Candida albicans has been detected with high frequency from the oropharyngeal candidiasis lesions of AIDS patients who have received repeated doses of fluconazole. In addition, most of such resistant strains also exhibit cross resistance to itraconazole and other azole drugs. Furthermore, the segregation of resistant strains has also been reported as to non-AIDS patients affected by chronic mucocutaneous candidiasis or deep candidiasis (Non Patent Document 3). The resistance problem has a serious impact on the management of ever-increasing deep mycosis patients (Non Patent Document 3).
Meanwhile, trichophytosis unguium caused by Trichophyton is one type of superficial mycosis and is an intractable disease that requires 3 to 6 months for its treatment. Oral agents of itraconazole and terbinafine are currently used as therapeutic drugs in the treatment of this disease. Under the present circumstances, both the drugs, however, produce an insufficient cure rate, albeit differing depending on reports, and recurrence has also been found (Non Patent Documents 4 and 5). In addition, terbinafine must be taken every day for 6 months, and poor compliance attributed to the long-term administration has therefore been pointed out for this drug (Non Patent Document 6). Both of these drugs also produce adverse reactions in approximately 10% or more cases and have been confirmed to have abnormality in clinical laboratory test results including liver function test results of approximately 5% patients. Itraconazole is known to exhibit interaction with many other drugs and is thus difficult to use in combination with other agents. In this regard, itraconazole is not selected as a therapeutic drug in some cases.
Accordingly, there is a strong demand for the emergence of a therapeutic drug for deep mycosis that is superior in safety and pharmacological effects on resistant fungi to existing drugs, a therapeutic drug for trichophytosis unguium that has a better cure rate and incidence of recurrence and a shorter dosing period than those of existing drugs, or a drug that has better safety or drug interaction than that of existing drugs.
A compound that has an amidine structure and is useful as an antiseptic (Patent Document 1) is disclosed. This compound is also useful as an antifungal agent against particular fungi according to the disclosure (Patent Document 2). Nonetheless, neither of the documents state that this compound also has an antifungal activity against Trichophyton. 